The roll change process couldn't be completed on time? There are 5 waiting points that can be dealt with without purchasing equipment.

Roll change is the most time-consuming task on the rolling line.

 

The plan was to complete the roll change in 40 minutes, but it actually took over an hour. The shift supervisor stood by, watching the clock, while the duty supervisor was sweating profusely due to the pressure, and the maintenance team was running around. After the roll change was done, the production output was reduced by a section. After the shift, they were criticized.

 

Where is the problem? Many people think it's due to "old equipment", "low automation level" or "insufficient manpower". But if you carefully break down the entire process of changing the rolls, you will find that the actual working time might only be for about 10-15 minutes, and the rest is all waiting.

 

The waiting points one after another, such as waiting for the step plates to be repeatedly calibrated, waiting for the roll system to be positioned and aligned, waiting for the oil and gas connectors to be inserted, waiting for the guide vanes to be adjusted, and waiting for the first signal. These waiting points consume time one after another.

 

If you don't purchase automatic roll changing equipment and don't invest a large amount of money for renovation, by eliminating these waiting points, it is completely possible to reduce the roll changing time by 20%-30%.

 

Today, let's break down these 5 hidden waiting points and provide standard on-site actions for each of them. 

 

1. First, let's break down the roll changing time:

Roll changing is not just two actions of "removing the old roll and installing the new one". It is a series of sequential steps. Roughly, it can be divided into the following sections:

 

Stage

 

Action content

 

Ideal time consumption

 

Prepare

 

The replacement rollers, spare parts, tools, and parameter sheets are all in place.

 

Before changing the rollers, complete the following tasks:

 

Remove the old ones

 

Loosen the locking mechanism, pull out the connection head, and remove the old rollers

 

5-8 minutes

 

Wait ①

 

Repeatedly adjust the stepwise pads

 

3 to 5 minutes

 

Install new

 

Push in new rollers, align, and lock.

 

5 to 10 minutes

 

Wait ②

 

Rolling system positioning swing

 

2 - 4 minutes

 

Wait ③

 

Oil and gas joint reinsertion/realignment

 

2 - 3 minutes

 

Wait ④

 

Guide and deflector serial adjustment

 

5 - 8 minutes

 

Wait ⑤

 

Waiting for the first signal/parameter confirmation before empty operation

 

3 to 5 minutes

 

Test drive

 

Point start, low speed, acceleration

 

3 to 5 minutes

 

In total, the ideal time is 25-35 minutes. But why does it always exceed the time? Because in the 5 "waiting periods", each one may double in time due to insufficient preparation.

 

Let's break it down one by one.

 

2. 5 hidden waiting points, each analyzed separately

Waiting point 1: Repeated calibration of the step pad

Situation: When the new roll is pushed in, locked, and the roll gap is measured, it is found to be incorrect. The lock is loosened, the step pad is replaced, then locked again, and the measurement is repeated - it takes two or three times before it is correct. Each time it takes 2-3 minutes, and the total time is over ten minutes.

 

Root cause: The height of the step pad was not calculated in advance. A step pad was taken and tested based on "the one used last time". The diameter of the working roll changed, the window of the frame was worn, the height of the bearing seat had a deviation, and yet the old data was still used, which definitely wouldn't match.

 

Standard action:

 

Before changing the roll, use a caliper to measure the diameter of the new roll and do not use the previous record

Based on the current roll diameter, the height of the bearing seat, and the depth of the window, calculate the required height of the step pad

Put the corresponding specification step pad on the roll changing cart in advance, without searching after the machine starts

Check the contact surface of the step pad: If the wear exceeds 0.5mm, replace it in advance, don't wait until after the machine starts to find it uneven and then remove it

?? Time-saving effect: Calculate and prepare in advance, this waiting point directly reduces from 3-5 minutes to 30 seconds (it is correct when put in).

Waiting point 2: Roll positioning oscillation

Situation: After the new roll is pushed in, the bearing seat and the window of the frame are not aligned. It swings left and right, moves forward and backward, and it takes two or three times of back and forth to be in place. Sometimes, a crowbar is needed to hold it in place.

 

Root cause: The positioning pin is worn, the guard plate is loose, there is accumulated iron oxide on the window, causing the positioning reference to be inaccurate. When pushing the roll, it is found by "feel" to locate the position, and the rate of one-time positioning is very low.

 

Standard action:

 

Before changing the roll, clean the iron oxide and oil stains in the window, especially the positioning surface and the guiding surface

Check if the positioning pin/protective plate is loose or worn, and handle it if it exceeds the tolerance

When pushing the roll, look at the marking line: Align the scale on the bearing seat with the benchmark line on the window, and push it in once

If the resistance when pushing increases abnormally, stop immediately and check if there are foreign objects or eccentricity, don't force push

?? Time-saving effect: Clean and check in advance, the rate of one-time positioning from 60% to over 90%, saving 2-4 minutes.

 

Waiting point 3: Reinserting the oil and gas connection

Situation: After roll positioning is completed, the fast-change connection for oil and gas lubrication is inserted. It is found that the model is incorrect, the sealing ring is damaged, it is not inserted properly, or after the test run, it is found to leak oil, and it is then removed and reinserted.

 

Root cause: The fast-change connection was not checked in advance, different frame connections were mixed, or the sealing ring was old and not replaced.

 

Standard action:

 

Before changing the roll, compare the oil and gas connection of the new roll bearing seat with the connection on the side of the frame

Replace the sealing ring in advance, don't wait until after it is inserted to find that it is leaking and then replace it

Clean the surface of the connection, without iron oxide and oil stains, to ensure it can be locked after being inserted

After completing the connection, quickly measure the ventilation condition with a portable air pressure gauge to confirm it is unobstructed before locking

?? Time-saving effect: Compare and replace the sealing ring in advance, avoid the cycle of "inserting and removing" after the machine starts, saving 2-3 minutes.

 

Waiting point 4: Serial adjustment of guide vanes

Situation: After the roll is changed and locked, the oil and gas connection is completed. Then the guide vanes are installed, the opening degree is adjusted, and the center line is adjusted. The roll changing and the adjustment of guide vanes are sequential - the previous task is completed before the next one can start, and they wait for each other.

 

Root cause: The adjustment of guide vanes and the roll changing are regarded as two independent tasks, and they are not arranged in parallel. In fact, many guide vanes actions can be carried out simultaneously during the roll changing process.

 

Standard action:

 

Before changing the roll, set the guide vanes to the "approximate value" - based on the new roll diameter and roll gap, calculate the opening degree of the guide vanes in advance, and do a rough adjustment first

After the old roll is withdrawn and the new roll is pushed in, use this gap to complete the rough positioning of the guide vanes

After the new roll is locked, only a fine adjustment is needed, no need to start from scratch

The guide vanes worker and the roll changing team communicate and coordinate the rhythm in advance, don't wait for each other

?? Time-saving effect: Switching from serial to parallel operation, the adjustment time for guide rails was reduced from 5-8 minutes to 2-3 minutes.

 

Waiting Point 5: Waiting for the first pass signal after changing the rolls

Situation: The rolls were changed, the guide rails were adjusted, but the rolling line had not given the signal yet, or the process parameters had not been confirmed. The operator sat at the control console and waited, and a few minutes passed.

 

Root cause: There was no prior communication between roll change and rolling line scheduling, and the roll change completion time and the rolling line rhythm were not aligned.

 

Standard action:

 

10 minutes before roll change, the shift supervisor and the opposite station confirm "The preparations are complete, when can you take over?"

Process parameters (roller gap, speed, tension, etc.) are input into the system in advance, and there is no need to fill them in after the roll change

The first pass signal conditions are confirmed in advance: roll temperature, rhythm interval, status of the preceding and following stands

After roll change, the operator directly confirms the signal, starts the test run by pressing the button, and does not wait for additional time

?? Time-saving effect: Communication in advance + parameter pre-setting, eliminating 3-5 minutes of ineffective waiting.

 

III. Preparation before roll change: Eliminate waiting before the machine starts

The common root cause of the 5 waiting points is that the preparatory work was not done in advance. Transform the following list into a fixed action before roll change, and most of the waiting will naturally disappear:

 

Serial Number

 

Preparation of the project

 

Completion time

 

Responsible person

 

1

 

Measurement of new roll diameter and calculation of step pad height

 

30 minutes before changing the roll

 

Assembly shift

 

2

 

Prepare the corresponding step pads and place the roller changing trolley.

 

20 minutes before changing the rollers

 

Assembly shift

 

3

 

Window cleaning, positioning pin/cover plate inspection

 

20 minutes before changing the rolls

 

Maintenance team

 

4

 

Oil and gas connection comparison, sealing ring replacement

 

20 minutes before changing the rolls

 

Lubrication worker

 

5

 

Adjust the guide rails to the approximate position

 

15 minutes before changing the rolls

 

Guide worker

 

6

 

Process parameter pre-input system

 

10 minutes before changing the rolls

 

Control panel

 

7

 

Communication and confirmation of rolling line rhythm

 

10 minutes before changing the rolls

 

Shift supervisor

 

8

 

Tools, spare parts, lifting equipment are in place

 

30 minutes before changing the rolls

 

Crane/Preparation Shift

 

IV. Even without purchasing equipment, several minutes can be saved on the landing sheet

Condense the above content into a "Roll Change Speed-up Comparison Table", and paste it on the wall of the duty room. Go through it each time before changing the rolls:

 

Waiting point

 

The original approach

 

Speeding up measures

 

Expected to save time

 

Step pad

 

After logging in, conduct repeated tests

 

Calculate and prepare in advance

 

3-4 minutes

 

Positioning

 

By feeling to push, repeatedly move

 

Clear the window, see the marking line at one go

 

2-3 minutes

 

Oil and gas joint

 

Plug it in and check if it's correct before replacing

 

Compare in advance, replace the sealing ring

 

2 minutes

 

Guide mechanism

 

After changing the rollers, re-adjust from the beginning

 

Parallel coarse adjustment and fine adjustment during roller replacement

 

3-4 minutes

 

First signal

 

After changing the rollers, wait without doing anything

 

Pre-communication + parameter presetting

 

3 minutes

 

In total

 

 

 

13-16 minutes

 

A 40-minute roller change process. Remove these 13-16 minutes and reduce it to 25 minutes or less. This saves about 10-15 minutes per shift. With several steel rolls per shift, over the course of a month, the actual output will be significantly increased.

 

 

Please provide a one-sentence summary.

The slow change of rolls is not due to a lack of manpower, nor is it because the equipment is too old. It is because there is too much waiting, too little parallel operation, and too late preparation.

 

Calculate the step pads in advance, position the pusher once, align the joints in advance, adjust the guide rails in parallel, and connect the signals in advance - without spending a penny on equipment, the time for changing the rolls can be reduced by a large margin.