Executive Summary
When a mid-size Bulgarian broiler feed producer faced inconsistent pellet quality and excessive die wear on their wheat-heavy formulation line, they turned to Hongyang Feed Machinery for a solution. By retrofitting their existing pellet mill with a Hongyang SZLH-series ring die engineered specifically for wheat-based broiler diets, the mill achieved a pellet durability index (PDI) of 97.5%, maintained stable throughput above 8 tonnes per hour, and extended die service life by approximately 40% compared to their previous supplier. This case study documents the technical assessment, implementation, and operational results of the partnership.
Customer Background
The client is a privately held feed manufacturer located in Stara Zagora Province, central Bulgaria — a region known as the country’s agricultural heartland. Operating a single-line pelleting facility with an annual production capacity of approximately 60,000 tonnes, the company supplies compound feed to over 40 contract broiler farms across southern and eastern Bulgaria. Their customer base includes both independent growers and several integrated poultry operations that demand strict adherence to EU feed safety and quality standards.
Bulgaria’s poultry sector has undergone significant modernization since the country joined the European Union in 2007. Domestic broiler production has grown steadily, reaching approximately 110,000 tonnes of live weight in recent years, driven by rising per-capita poultry consumption and export opportunities to neighboring markets including Romania, Greece, and North Macedonia. This growth has placed pressure on feed manufacturers to deliver consistent pellet quality while controlling production costs.
The client operates a European-manufactured pellet mill originally rated at 10 t/h. Their standard broiler formulation contains approximately 55–60% wheat, 15–20% soybean meal, 5–8% sunflower meal (a locally abundant by-product), and supplementary fats, minerals, and amino acids. Wheat-dominant diets present a well-documented pelleting challenge: wheat starch gelatinizes at a higher temperature than corn starch, and without precise control of steam conditioning and die specifications, pellet durability suffers.
The Challenge
Over a six-month period in early 2025, the mill’s production team documented three interconnected problems with their existing ring die:
1. Declining PDI.
Routine quality checks showed pellet durability dropping from an acceptable 95.5% to as low as 91.2% by the third month of die use. Fines accumulation at the cooler discharge and in-farm feeding systems increased measurably, prompting complaints from several contract growers about feed wastage and uneven intake in automated pan-feeding lines.
2. Throughput Instability.
To compensate for declining pellet quality, operators consistently increased steam addition and adjusted roll gap, but these interventions caused throughput to oscillate between 6.2 and 8.8 t/h. The erratic production rate complicated downstream batching and increased energy consumption per tonne.
3. Accelerated Die Wear.
The previous ring die, supplied by a generic manufacturer, required replacement after approximately 1,800 operating hours — well below the industry benchmark of 2,500–3,000 hours for wheat-based broiler diets. Die bore wear was visibly uneven, with premature scoring concentrated in the inner ring zone.
A root-cause analysis conducted jointly by the mill’s production manager and an external feed technology consultant identified the die metallurgy and compression ratio as the likely culprits. The previous die used standard-grade chrome steel with a uniform compression ratio that did not account for the higher friction characteristics of wheat starch and the abrasive nature of sunflower meal fibers.
Hongyang’s Solution
The client contacted Hongyang Feed Machinery through an industry referral from a Bulgarian equipment distributor who had previously sourced spare parts from Chinese manufacturers. After reviewing the mill’s formulation data, production logs, and die wear photographs, Hongyang’s technical team proposed a tailored ring die solution:
Die Specifications:
| Parameter | Previous Die | Hongyang HYPM Die |
|---|---|---|
| Material | Standard chrome steel (12% Cr) | High-chromium alloy steel (20% Cr, 2.2% C) |
| Die inner diameter | 520 mm | 520 mm (direct retrofit) |
| Effective width | 180 mm | 180 mm |
| Hole diameter | 3.5 mm | 3.5 mm |
| Compression ratio (L/d) | 10.0 (uniform) | 10.5 (optimized for wheat-based diets) |
| Heat treatment | Single-stage vacuum hardening | Double-stage vacuum hardening + cryogenic treatment |
| Surface hardness | 58–60 HRC | 62–64 HRC (core 58–60 HRC) |
| Hole finish | Standard gun-drilled | Gun-drilled + precision honed (Ra ≤ 0.8 µm) |
Key Technical Differentiators:
The Hongyang die featured a slightly higher effective compression ratio (10.5 vs. 10.0), calculated to optimize starch gelatinization for wheat-dominant formulations without over-compressing and generating excessive frictional heat. The die relief configuration — featuring a tapered inlet and stepped relief in the final 3 mm of each hole — was designed to produce a denser, more durable pellet surface while maintaining throughput.
The double-stage vacuum hardening process, combined with deep cryogenic treatment at -120°C, transformed retained austenite in the steel matrix to martensite, yielding a finer, more uniform carbide distribution. This metallurgical approach directly addressed the abrasive wear caused by sunflower meal fibers — a formulation component that is both economically important in the Black Sea region and notoriously hard on pelleting equipment.
Installation was performed by the client’s in-house maintenance team during a scheduled weekend shutdown. The Hongyang die was a direct drop-in replacement for the existing 520 mm die, requiring no modifications to the pellet mill frame, roll assembly, or drive system. Total installation time was under six hours.
Results
The Hongyang ring die was commissioned in October 2025. Production data collected over the subsequent four months (October 2025 – January 2026) showed measurable improvements across all key performance indicators:
| Metric | Before (Previous Die) | After (Hongyang HYPM) | Improvement |
|---|---|---|---|
| Average PDI (%) | 93.5 (declining) | 97.5 (stable) | +4.0 points |
| Fines at cooler discharge (%) | 6.8% | 2.2% | -68% |
| Stable throughput (t/h) | 6.2–8.8 (unstable) | 8.1–8.6 (stable) | Range narrowed by 83% |
| Average throughput (t/h) | 7.5 | 8.3 | +11% |
| Specific energy (kWh/t) | 14.2 | 13.1 | -7.7% |
| Die service life (hours) | ~1,800 | ~2,500 (extrapolated) | +39% |
| Grower complaint rate | 2.3/month | 0.4/month | -83% |
Pellet Quality Stability. The most significant outcome was the consistency of pellet quality across the die’s service life. Monthly PDI measurements at the four-month mark remained at 97.3%, with no evidence of the early-stage degradation pattern observed with the previous die.
Feed Conversion Feedback. Three of the largest contract farms reported improved feed conversion ratios (FCR) averaging 1.62–1.64 in the first four months after the die change, compared to 1.66–1.69 in the preceding period. While multiple factors influence FCR, the reduction in fines and improved pellet integrity were identified by both the mill and farm nutritionists as contributing variables.
Operator Experience. The mill’s shift supervisors reported significantly reduced need for mid-shift roll gap adjustments and steam valve corrections. The narrower throughput band allowed more predictable scheduling of downstream mixing, cooling, and load-out operations.
Customer Feedback
The production manager at the Bulgarian mill commented on the partnership in a follow-up review conducted in February 2026:
We were initially cautious about sourcing from a Chinese manufacturer, given our past experience with generic suppliers. The difference with Hongyang was evident from the first week — the die ran smoothly, the pellet quality was immediately better, and most importantly, it stayed consistent. The technical documentation and die specification rationale they provided before shipment gave us confidence that this was not a generic product, but a genuinely engineered solution for our specific formulation.
The mill has since placed orders for two additional Hongyang ring dies — one for their backup pellet mill and a spare for the primary line — and is evaluating Hongyang roller shells for the same application.
Conclusion
This Bulgarian case demonstrates that a well-specified ring die, manufactured with appropriate metallurgy and engineered to the specific demands of regional feed formulations, can deliver tangible improvements in pellet quality, production stability, and operating cost. For Hongyang Feed Machinery, the engagement reinforced the value of pre-sale technical analysis and the importance of treating each customer’s formulation as a unique engineering challenge rather than a one-size-fits-all product sale.
As Eastern European feed manufacturers continue modernizing their operations and raising quality standards to compete in the EU market, demand for precision-engineered pelleting components is expected to grow — and Hongyang is positioned to meet that demand with data-driven, application-specific solutions.
Hongyang Feed Machinery Co., Ltd. is a specialized manufacturer of ring dies, roller shells, and pellet mill components for the animal feed, aquafeed, and biomass industries. Based in Liyang, Jiangsu Province, China, the company serves customers in over 40 countries worldwide.
Post time: Jun-16-2026
