Abrasives Tips 3
About the test of abrasives
The test of grinding aid includes small grinding test and large grinding test, which is an important measure to ensure the suitability of grinding aid and reduce the cost of selection.
The purpose of the small grinding test is: to use the material (the material being used or the material to be used) to initially select the variety and dosing of the grinding aid; to use the material to initially verify the adaptability of the grinding aid (mineral composition, ease of grinding) to reduce the blindness of the large grinding test; to use the standard material (self-matching) to verify the stability of the grinding aid in use.
The purpose of the large grinding test is to further verify the adaptability of the primary grinding aid to the grinding conditions on the basis of the small grinding test. Factors affecting the adaptability of grinding aids such as the ease of grinding, adhesion, moisture, temperature, etc., the grinding conditions of ventilation, grinding temperature, grading, etc., quality control indicators such as fineness, specific surface area, particle grading, gypsum dosing, etc., the use of performance of water demand, water retention, compatibility with additives, etc.
Although the use of the test before the use of abrasives is very important, but repeated tests, especially the large grinding test, not only to consume a lot of manpower, but also a large impact on production, test costs are higher, which is one of the reasons why many companies are reluctant to do large grinding test.
In fact, except for special needs, we can choose an adaptable grinding aid as a comparison grinding aid at the beginning of the big grinding test, and replace the blank test with a comparison grinding aid test in the subsequent big grinding test, which can reduce the impact of the big grinding test of grinding aid.
3.1 Small grinding test of grinding aid
After each batch of grinding aid comes into the factory, a small grinding comparison test should be conducted, and if there is abnormal data, another small grinding test should be done or a large grinding test should be arranged, and at the same time, contact with the grinding aid business to solve the problem and identify the causes.
(1) Raw material preparation: clinker, natural gypsum, and various mixed materials required for the test are randomly taken as normal samples in the cement mill head (or yard), crushed to particle size <7mm, dried and mixed evenly.
Test cement clinker requirements: 3d compressive strength ≥ 28MPa, 28d compressive strength ≥ 56MPa, C3S ≥ 55%, C3S + C2S ≥ 75%, f-CaO ≤ 1.5%, test small mill cement material integrated moisture ≤ 1.5%.
In order to improve the comparability of test results, as well as the large mill test, the guidance of the use of large mill, the clinker used in the test is required to prepare once a month, mixed materials prepared quarterly, gypsum prepared once every six months, mixed evenly spare, sealed and stored.
(2) Preparation of standard cement samples: according to the average actual material (dry basis) ratio of the variety of cement in the previous month, mix the same proportion of grinding aid on the experimental small mill as the actual production (last batch of grinding aid), grind to the actual quality control index of the company, and make 5kg standard cement samples.
(3) Preparation of comparison cement samples: the same ratio as the standard test cement material, mixed with the same grinding aid, the same amount of grinding aid and grinding time, and 5kg of comparison cement samples are made.
(4) Test and comparison: The following items can be tested and compared between the two samples: grinding time, chloride ion, alkali content, sulfur trioxide, loss of burn, water consumption of standard consistency, setting time, 80μm sieve, specific surface area, stability, 3 d strength, 28 d strength, flow rate. When comparing the cement sample with the standard sample, the difference of 3d compressive strength is within ±0.8MPa and there is no obvious abnormality in other items, it can be considered that the batch of grinding aid is of the same quality as the previous batch of grinding aid.
3.2 Large grinding comparison test of grinding aid
In principle, cement enterprises using grinding aids should conduct at least one large grinding comparison test every quarter, and when there are objections to the quality of grinding aids, they can conduct large grinding tests at any time according to their actual situation and needs. The quality of the cement produced by the blank test and the large grinding test must meet the cement quality control standard requirements of the cement enterprise.
The procedure of the large grinding test is relatively complex and requires close cooperation of the production system of the cement enterprise, so we must pay attention to the organization of the test. It is recommended that the quality control department of the cement enterprise should take the lead and make a detailed test plan, and after the approval of the production leader, convene the relevant units of the cement enterprise and the grinding aid business to meet together and make detailed arrangements, so as to do the preparatory work before the test.
The large grinding test shall be conducted under normal and stable conditions of material quality and grinding conditions. For the system that has used grinding aid, in order to ensure that the quality indexes of the blank test cement samples meet the requirements of the internal control standard, the mixture ratio should be adjusted before stopping the grinding aid, in principle, the total amount of mixed materials should be adjusted downward by not less than 6%, and the species of mixed materials should be the maximum amount of mixed materials, and the table time output should be adjusted downward by 5% to 10%, which should be adjusted in place step by step, and the grinding aid should be stopped after 30 minutes of material adjustment. Grinding aid.
After the mill conditions are stable and the cement quality control indicators are qualified for 2h, the cement is continuously sampled for more than 4h, with a sample size of not less than 10kg. the sample is mixed evenly and passed through 0.9mm sieve, as a blank sample for large grinding test, and the sample is sealed in three parts, one for each unit and grinding aid business, and one for arbitration.
(2) Use of abrasive test
After the blank test sample is finished, add the test grinding aid under the premise of keeping the mill ratio and feeding quantity unchanged. According to the agreed model and dosing amount between the supply and demand sides to join, require every 30min to join the amount of calibration, such as the error exceeds 5.0%, should be adjusted in a timely manner, and make records.
After the mill condition is stable and the cement quality control indexes are qualified for 1h, in principle, gradually adjust the total amount of mixed materials by not less than 6%, adjusting the mixed materials for the blank test, adjusting the output by 5% to 10%, requiring step-by-step adjustment in place, this process requires 3~4h.
After the mill condition is stable, continuous sampling for 4h, the sampling volume is not less than 10kg, the sample taken will be mixed and passed through 0.9mm sieve, as the sample of grinding aid for large grinding test, the sample will be mixed and left after the comparison sample. The sample is divided into three copies and sealed, one for the use of units, one for the business of abrasives for inspection, and one for arbitration.
3)Inspection and comparison
After the end of the test, the user of the abrasives and the business should promptly carry out the sample test, the test content of the blank test and the use of abrasives test two samples can refer to the test items of the small grinding test samples, complete the test report and interchangeable confirmation. If the user and the businessman of the abrasive aid disagree on the test results, they can agree to re-test or take the third-party arbitration approved by both parties.
4)Cautions for large grinding test
To strengthen the monitoring and management of the cement for the large grinding test, the cement produced must meet the requirements of the enterprise's cement quality control standards. The cement produced during the big grinding test must enter the cement warehouse designated by the user's quality control department, and the quality control department should strengthen the monitoring and frequency of the batch of cement, and only after the 1d strength and the rest of the quality control indexes have passed the test can be matched with the homogenized factory.